Typically, a corner bead for trimming a drywall corner has a central portion with two lateral edges and two flange portions, each extending from one of the lateral edges of the central portion.
It is also known to provide the flange portions with an array of apertures, either circular apertures or elongated slots, whereby the "mud", when pressed onto the outer surface of the flange portions, can be thus pressed through the apertures or holes and into intimate contact with the underlying drywall. When pressed through the apertures such material or "mud" bonds with and helps to attach the corner bead to the underlying drywall.
Commonly, the central portion has an arcuate profile and defines a convex surface and a concave surface, whereupon the convex surface becomes the outer surface in use. If the convex surface has a large radius, for example within the range of from about 0.375 to about 1.5 inches, it is commonly known as a "bullnose" corner bead.
Weldy, U.S. Pat. No. Re. 34,547 discloses various corner beads, two-way and three-way corners having central portions with an arcuate profile and having two flange portions.
Koenig et al, U.S. Pat. No. 5,752,353 describes a drywall trimming article having an arcuately profiled, elongated central portion and two flange portions that are extruded unitarily. Each flange has a series or array of apertures as described above. In the case of Koenig et al, the outer surface of the corner bead is coated with a fibrous material to promote adhesion of the subsequently applied "mud".
In installation, the corner bead is typically stapled or glued to the drywall corner prior to application of the dry wall finishing material or "mud" to maintain the positioning of the corner bead during "mud" application. The gluing or stapling can be a time consuming process in an otherwise rapid application process Additionally, most drywall corners are not perfectly square. Consequently, alignment of the corner bead with the underlying drywall corner can be difficult. Furthermore, failure to so attach the corner bead to the corner prior to "mud" application can result in slippage or movement of the corner bead from its proper location during such installation.
The simplification of the corner bead alignment with the underling drywall corner is often accomplished through the use of relatively complex and/or relatively expensive power tools that assist with alignment while stapling or gluing the corner bead to the underlying drywall The elimination of the use of such tools or the stapling or gluing operation entirely, would be of great value to the drywall installer in terms of time and cost. The mere ability to rapidly achieve corner bead alignment with the underlying drywall corner is of great value for the same reasons, even if stapling or attachment is still performed.